Field of the Invention
The present invention relates to a solid electrolytic capacitor element, and a method for manufacturing a solid electrolytic capacitor and a solid electrolytic capacitor element.
Priority is claimed on Japanese Patent Application No. 2014-248882, filed Dec. 9, 2014, the content of which is incorporated herein by reference.
Description of Related Art
Solid electrolytic capacitor elements are composed of an anode body formed from a conductor such as a sintered body of a valve action metal powder, a dielectric layer of a metal oxide formed on the surface of the anode body by subjecting the surface of the anode body to electrolytic oxidation in an aqueous solution of an electrolyte such as phosphoric acid, and a cathode formed from a conductive polymer semiconductor layer of a conductive polymer formed on the dielectric layer by electrolytic polymerization or the like and a conductor layer formed on the conductive polymer semiconductor layer.
Examples of known methods for forming the conductive polymer semiconductor layer include methods using a low-viscosity polymerization solution such as a chemical polymerization method or an electrolytic polymerization method, and methods in which the anode body that has been coated with the dielectric layer is dipped in a high-viscosity conductive polymer dispersion. Using a low-viscosity solution is superior in terms of enabling the semiconductor layer to be formed even within very confined portions of the porous structure of the anode body, but also suffers some problems, including a low density for the formed semiconductor layer, and a potential increase in short circuits and the leakage current (LC). On the other hand, using a high-viscosity conductive polymer dispersion is superior in terms of enabling the formation of a high-density semiconductor layer, but suffers from different problems, including an inability to form the conductive polymer semiconductor layer in very confined portions, and an inability to obtain satisfactory adhesion.
In order to address these problems, Patent Document 1 discloses a method in which the conductive polymer semiconductor layer is formed as two layers, using a low-viscosity solution for forming the first conductive polymer semiconductor layer, and using a high-viscosity solution for forming the second conductive polymer semiconductor layer.
In recent years, in order to enhance the performance of solid electrolytic capacitors, investigations have also been conducted into the valve action metal used for the anode body. For example, Patent Document 2 discloses a solid electrolytic capacitor which uses a sintered body of a tungsten powder for the anode body. A solid electrolytic capacitor which uses a sintered body of a tungsten powder for the anode body is able to manufacture a larger capacitance than solid electrolytic capacitors which use sintered bodies of other valve action metals. However, cracking of the dielectric coating during the chemical conversion step, and a large leakage current tend to be problematic, and investigations are ongoing.